In the region between the plates, the electron moves with an acceleration $\vec{a}$ given by : (A) $-(3.5 \times 10^{15} \text{ ms}^{-2}) \hat{k}$ (B) $(3.5 \times 10^{15} \text{ ms}^{-2}) \hat{k}$ (C) $(3.5 \times 10^{13} \text{ ms}^{-2}) \hat{i}$ (D) $-(3.5 \times 10^{13} \text{ ms}^{-2}) \hat{i}$